Project Summary Uterine leiomyomas (fibroids) are a devastating disorder for millions of women, who experience morbidity from heavy bleeding, pelvic pain, or reproductive problems. They disproportionately impact Black women in the United States. Progress in identifying risk factors and nonsurgical treatment for fibroids has been slow. One reason is reliance on ultrasonography for diagnosis and monitoring, which is highly operator dependent, has poor accuracy in women with multiple fibroids, and provides no molecular information about tumor(s). Our study will address the critical need to identify sensitive, and specific, mechanistic biomarkers that can help assess fibroid presence, progression, and potential for future growth through non-invasive means. We will focus on microRNAs (miRNAs), non-coding RNAs that are highly expressed in fibroid tumor cells and participate in mechanisms that drive fibroid development by profiling microRNAs packaged in extracellular vesicles (EV-miRNAs). Circulating EV-miRNAs can be measured non-invasively in plasma and have unique properties that make them suitable for liquid biopsy applications in research and clinical settings. The long-term goal of this research is to identify non-invasive biomarkers that can predict fibroid growth and progression. The objective of the proposed study is to identify EV-miRNAs related to fibroid presence and characterize their association with clinical measures of disease burden in a racially diverse population. Our central hypothesis is that a specific pattern of EV miRNAs will be a valid, mechanistic biomarker of fibroid presence and disease burden. This hypothesis was developed based on strong preliminary data and will be tested through 2 specific aims. In Aim 1, we propose to establish the relationship between EV-miRNA signatures in plasma and presence of fibroids using data from 50 women having a hysterectomy for fibroid treatment and 50 controls having a hysterectomy for pelvic pain or heavy bleeding with no fibroids. In Aim 2, we propose to characterize the association of plasma EV-miRNA expression and disease burden, measured by fibroid size and menstrual bleeding severity, among 50 women having a hysterectomy for fibroid treatment (cases from Aim 1) and 100 women with newly detected fibroids, who typically have less severe symptoms and smaller fibroids. The innovative aspects of our proposal include: the study of EV-miRNAs in fibroids, the multidisciplinary study team, the overall approach, and the development of liquid biopsy tools. Our proposed study is responsive to the research priorities of NICHD Gynecologic Health and Disease Branch, which promote the development of novel biomarkers for fibroids and other gynecologic disorders. This contribution is significant because it will advance fibroid etiologic research by enabling large, prospective studies of fibroid outcomes with repeated, mechanistic biomarker measurements. The anticipated outcomes of our proposed study have the potential to transform fibroid research and clinical care and may catalyze development of individualized treatments. These advancements will decrease the public health burden of fibroids and improve minority health.